Synaptic proliferation in the auditory cortex of the young adult rat following callosal lesions

Summary The long-term effects of partial deafferentation in the neocortex of adult rats were studied in four-month old rats in which the corpus callosum had been completely sectioned when they were one-month old. Quantitative light microscopy was used to identify morphological changes in the auditory cortex resulting from the loss of established callosal connections. Particular attention was directed at those cortical layers known to receive the heaviest callosal projection (layers II and III) and at neurons known to be postsynaptic to callosal afferents (layer V pyramidal neurons). The comparative analysis of both semithin plastic sections and Golgi-impregnated material from long-term, callosally-lesioned rats and age-matched control animals reveals no differences in the overall cortical thickness, the thickness of cortical layers, the numbers of neurons or the density of spines along apical dendrites of layer V pyramidal neurons. However, as a result of the callosal lesion, large diameter apical dendrites are significantly thinner in the callosally deafferented cortex and there is a small increase in the number of neuroglial cells in the deeper cortical layers.